Had a pretty clear looseness indication come through on a felt roll bearing (drive side)on a paper machine.

Decided to shut the machine and change the roll. When we pulled the bearing end cover off, we found the withdrawal sleeve had come loose, and walked out from under the bearing. Interestingly, the lock-nut was still in place.

We monitor this fortnightly, and I guess that this thing was going to die in a rather ugly (and expensive)way in the next few hours. if the reading had been taken the day before, we probably would have missed it.

Sometimes, fate smiles on you....


Ian

sleeveloose.doc (246 Kb, 81 downloads)

Yes you were "lucky" indeed.

Could you tell if the bearing locked up and caused all this damage to the sleeve or did the sleeve just work loose? Seems like, with the nut still being in place, the sleeve would not have been destroyed so severely unless the bearing was locked and "ripped" the sleeve loose, huh?

Ralph,
The bearing itself was fine - hardly a mark on it. The grease was pretty dry, but I figure that was due to the heat generated once it started to spin.

I think the sleeve just worked loose. Don't know why - this roll had been happily trundling along for over 7 years.


Ian

Talked to a paper machine mechanic today about this excellent case. Two things were pointed out. When the bearing was installed, there could have been a small fragment in the surfaces inside and outside the cone which prevented a full seating surface with all that available steel to steel friction coefficient 0.15. It took 7 years to make that fragment deteriorate or work itself into the surface so the friction for turning was low enough to accept an initial micro movement. The rest is history. (When the surfaces are cleaned to install here, we rub it always only in axial direction with fine paper and clean out more than careful.) The other aspect is if the unit has been subject to a quick heating up recently. If all is cold and you start so fast that the usual temperature rise is not all evenly through, the outer ring (actually the brg inner) can grow and release the fit to allow a micro motion. This is a known problem here, caused by the increased eagerness the shift has to get all up rolling after a cleaning stop. Just some meat for talks, regards Arne

Thanks Arne,
I'm not aware that the start-up operation has been significantly different recently, but I don't see what the operators do; especially on nightshift.

We have done a lot of work to educate the roll shop fitters about the importance of correct fitment; they used to flog the bearings up with a hammer; they now have hydraulic nuts to take up clearances, and pay a lot of attention to sizes and shaft condition etc.

This has given far better reliability, but we still get the occasional (once a year or so) failure like this. Sometimes, we are fortunate enough to find it before lots of damage is done. Other times, we are not so lucky.....

Thanks for the replies.

Ian